The present invention relates to a refrigerating system, and particularly relates to a binary refrigerating system including a low stage side refrigerant circuit and a high stage side refrigerant circuit.
A binary refrigerating system has been conventionally used as a refrigerating system for a cold storage, a thermal-shock testing system or the like. The binary refrigerating system is constituted by a low stage side refrigerant circuit and a high stage side refrigerant circuit which are connected to each other through a cascade condenser as disclosed in Japanese Unexamined Patent Publication Gazette No. 9-210515.
With reference to FIG. 13, the conventional binary refrigerating system (200) will be now described. The low stage side refrigerant circuit (202) is formed by connecting a low stage side compressor (207), a cascade condenser (206), a low stage side receiver (208), a low stage side expansion valve (204) and an evaporator (209) in this order, while the high stage side refrigerant circuit (203) is formed by connecting a high stage side compressor (210), a condenser (212), a high stage side receiver (211), a high stage side expansion valve (205) and the cascade condenser (206) in this order. Further, in the conventional binary refrigerating system (200), the expansion valves (204) and (205) of the high stage side refrigerant circuit (203) and the low stage side refrigerant circuit (202) are each constituted by a temperature-sensitive thermostatic expansion valve (hereinafter, referred to as a temperature-sensitive expansion valve) Furthermore, the cascade condenser (206) is constituted by a double-pipe heat exchanger.
In the high stage side refrigerant circuit (203), a high stage side refrigerant discharged from the high stage side compressor (210) develops such circulation as to condense in the condenser (212), reduce its pressure in the high stage side expansion valve (205), evaporate in the cascade condenser (206) and return to the high stage side compressor (210). On the other hand, in the low stage side refrigerant circuit (202), a low stage side refrigerant discharged from the low stage side compressor (207) develops such circulation as to condense in the cascade condenser (206) to recover cold heat from the high stage side refrigerant, reduce its pressure in the low stage side expansion valve (204), evaporate in the evaporator (209) to cool substance to be cooled (ex., air), and return to the low stage side compressor (207).
Meanwhile, at the time of start-up of the system (200), the temperature in the cascade condenser (206) may not be decreased down to a predetermined condensation temperature for the low stage side refrigerant. For example, if the system (200) has been shut down for a long time, the temperature in the cascade condenser (206) rises up to around ordinary temperatures. Therefore, if the high stage side compressor (210) and the low stage side compressor (207) are started up at the same time, the low stage side refrigerant circuit (202) may be excessively raised in its high pressure, resulting in operation of a protective device such as a high-pressure switch in spite of the system (202) being in normal conditions. To cope with this and prevent such unintended behavior of the protective device, the system is generally arranged so that the high stage side compressor (210) is started up ahead of start-up of the low stage side compressor (207) and after the expiration of a certain period the low stage side compressor (207) is started up.
For the binary refrigerating systems, it is important to stabilize the high pressure in the low stage side refrigerant circuit (202) since their performance is determined mainly depending upon operating conditions of the low stage side refrigerant circuit (202). In the conventional binary refrigerating system, however, the temperature-sensitive expansion valve (205) is used for the high stage side refrigerant circuit (203) and therefore it takes a considerably long time (for example, about 5 minutes) to stabilize the superheating degree of the high stage side refrigerant at the outlet of the cascade condenser (206) after the start-up of the high stage side compressor (210). Accordingly, there has been a problem in the conventional binary refrigerating system in that even if the low stage side compressor (207) is started up behind a certain period, the temperature-sensitive expansion valve (205) cannot response to an abrupt increase in load resulting in operation of the protective device of the low stage side refrigerant circuit (202).
Particularly for a so-called multi-system equipped with low stage side refrigerant circuitry constituted by a plurality of pipelines including a plurality of low stage side compressors, respectively, if the number of low stage side compressors started up is changed, the temperature-sensitive expansion valve (205) of the high stage side refrigerant circuit (203) cannot response to load variations of the low stage side refrigerant circuit so that the protective device of the low stage side refrigerant circuit easily operates.
The present invention has been made in view of this problem and therefore its object is to improve operational responsiveness of the high stage side refrigerant circuit to the low stage side refrigerant circuit.
To attain the above object, the present invention employs a motor-operated expansion valve as an expansion mechanism in the high stage side refrigerant circuit and provides for controlling the motor-operated expansion valve so that the high pressure in the low stage side refrigerant circuit reaches a target high pressure. In other words, the present invention provides for controlling the expansion mechanism of the high stage side refrigerant circuit based on the conditions of the low stage side refrigerant circuit.
More specifically, a first invention is directed to a refrigerating system, which comprises: a high stage side refrigerant circuit (3, 120) formed by connecting a high stage side compressor (9, 18, 121), a condenser (10, 122), a motor-operated expansion valve (12, EVL1, EVL2) and a refrigerant heat exchanger (5, 111A, 111B) in this order; a low stage side refrigerant circuit (2, 103A, 103B) formed by connecting a low stage side compressor (4, 31A, 31B, 131A, 131B), the refrigerant heat exchanger (5, 111A, 111B), an expansion mechanism (7, EV21) and an evaporator (8, 50) in this order; a high-pressure sensing means (SPH2), provided in the low stage side refrigerant circuit (2, 103A, 103B), for sensing the high pressure in the low stage side refrigerant circuit (2, 103A, 103B); and an expansion valve control means (16) for controlling the motor-operated expansion valve (12, EVL1, EVL2) of the high stage side refrigerant circuit (2, 120) so that the pressure sensed by the high-pressure sensing means (SPH2) reaches a predetermined target high pressure.
With this arrangement, in the high stage side refrigerant circuit (3, 120), a high stage side refrigerant develops such circulation as to be discharged from the high stage side compressor (9, 18, 121), condense in the condenser (10, 122), reduce its pressure in the motor-operated expansion valve (12, EVL1, EVL2), evaporate in the refrigerant heat exchanger (5, 111A, 111B) and return to the high stage side compressor (9, 18, 121). On the other hand, in the low stage side refrigerant circuit (2, 103A, 103B), a low stage side refrigerant develops such circulation as to be discharged from the low stage side compressor (4, 31A, 31B, 131A, 131B), exchange heat with the high stage side refrigerant in the refrigerant heat exchanger (5, 111A, 111B) to condense, reduce its pressure in the expansion mechanism (7, EV21), evaporate in the evaporator (8, 50) for cooling substance to be cooled, and return to the low stage side compressor (4, 31A, 31B, 131A, 131B). The motor-operated expansion valve (12, EVL1, EVL2) of the high stage side refrigerant circuit (3, 120) is controlled directly for the low stage side refrigerant circuit (2, 103A, 103B) so that the high pressure in the low stage side refrigerant circuit (2, 103A, 103B) which is sensed by the high-pressure sensing means (SPH2) reaches the predetermined target high pressure, and operational responsiveness of the high stage side refrigerant circuit (3, 120) to the low stage side refrigerant circuit (2, 103A, 103B) is thereby improved.
A second invention is concerned with the first invention, wherein the system further comprises: a temperature sensing means (Tx) for sensing the temperature of the substance to be cooled by the evaporator (8, 50); and a target high pressure setting means (23) for setting the target high pressure of the expansion valve control means (16) based on the temperature sensed by the temperature sensing means (Tx).
With this arrangement, the target high pressure in the low stage side refrigerant circuit (2, 103A, 103B), which provides a standard for control of the motor-operated expansion valve (12, EVL1, EVL2), is adequately set based on the temperature of the substance to be cooled. As a result, the control of the motor-operated expansion valve (12, EVL1, EVL2) can be made in flexible response to load.
A third invention is concerned with the first invention, wherein the system further comprises: a low pressure sensing means (SPL2), provided in the low stage side refrigerant circuit (2, 103A, 103B), for sensing the low pressure in the low stage side refrigerant circuit (2, 103A, 103B); and a target high pressure setting means (23) for setting the target high pressure of the expansion valve control means (16) based on the pressure sensed by the low pressure sensing means (SPL2).
With this arrangement, the target high pressure in the low stage side refrigerant circuit (2, 103A, 103B), which provides a standard for control of the motor-operated expansion valve (12, EVL1, EVL2), is adequately set based on the low pressure in the low stage side refrigerant circuit (2, 103A, 103B). As a result, the control of the motor-operated expansion valve (12, EVL1, EVL2) can be made in flexible response to load.
A fourth invention is concerned with the first invention, wherein the system further comprises: a temperature sensing means (Tx) for sensing the temperature of the substance to be cooled by the evaporator (8); a low pressure sensing means (SPL2), provided in the low stage side refrigerant circuit (2), for sensing the low pressure in the low stage side refrigerant circuit (2); a transient state detecting means (23a) for determining whether the operation of the system is in a transient state based on preset particular determination conditions and outputting a predetermined transient state signal upon detection of the transient state or outputting a predetermined non-transient state signal upon detection of a non-transient state; and a target pressure setting means (23) for setting upon receipt of the transient state signal the target high pressure of the expansion valve control means (16) based on the temperature sensed by the temperature sensing means (Tx) or setting upon receipt of the non-transient state signal the target high pressure based on the pressure sensed by the low pressure sensing means (SPL2).
With this arrangement, the target high pressure is set based on the temperature of the substance to be cooled when the operation is in a transient state, or the target high pressure is set based on the low pressure in the low stage side refrigerant circuit (2) when the operation is in a non-transient state, i.e., steady.
A fifth invention is concerned with the first invention, wherein the system further comprises: a superheating degree detecting means (27) for sensing the superheating degree of a suction gas refrigerant of the high stage side compressor (18, 121) in the high stage side refrigerant circuit (3, 120); and the expansion valve control means (16) being arranged to control the motor-operated expansion valve (12, EVL1, EVL2) of the high stage side refrigerant circuit (2, 120) so that the pressure sensed by the high-pressure sensing means (SPH2) and the superheating degree sensed by the superheating degree detecting means (27) reach a predetermined target high pressure and a predetermined target superheating degree, respectively.
With this arrangement, the motor-operated expansion valve (12, EVL1, EVL2) is controlled so that the high pressure in the low stage side refrigerant circuit (2, 103A, 103B) reaches the target high pressure and the superheating degree of the suction gas refrigerant of the high stage side compressor (9, 121) in the high stage side refrigerant circuit (3, 120) reaches the target superheating degree. As a result, the high stage side compressor (9, 121) can be protected from liquid back and the like and at the same time the high pressure in the low stage side refrigerant circuit (2, 103A, 103B) can be held at a suitable value.
A sixth invention is concerned with the fifth invention, wherein the system further comprises: the expansion valve control means (16) being set to calculate a first amount of change of opening (xcex94EV1) based on the pressure sensed by the high-pressure sensing means (SPH2), calculate a second amount of change of opening (xcex94EV2) based on the superheating degree sensed by the superheating degree detecting means (27) and change the opening of the motor-operated expansion valve (12) of the high stage side refrigerant circuit (3) based on the first amount of change of opening (xcex94EV1) and the second amount of change of opening (xcex94EV2); and a setting change means (22b) for changing the setting of the expansion valve control means (16) so that the expansion valve control means (16) changes the opening of the motor-operated expansion valve (12) solely based on the second amount of change of opening (xcex94EV2) when the sensed superheating degree is a value beyond a predetermined range and the first amount of change of opening (xcex94EV1) is positive.
With this arrangement, the opening of the motor-operated expansion valve (12) in the high stage side refrigerant circuit (3) is changed in principle based on the first amount of change of opening (xcex94EV1) calculated based on the high pressure in the low stage side refrigerant circuit (2) and the second amount of change of opening (xcex94EV2) calculated based on the superheating degree of the suction gas in the high stage side refrigerant circuit (3). When the superheating degree of the suction gas is a value beyond the predetermined range and the first amount of change of opening (xcex94EV1) is positive, the opening of the motor-operated expansion valve (12) is exceptionally changed based on the second amount of change of opening (xcex94EV2) alone.
A seventh invention is concerned with the first invention, wherein the system further comprises: a superheating degree detecting means (27) for sensing the superheating degree of a suction gas refrigerant of the high stage side compressor (121) in the high stage side refrigerant circuit (120); a discharge gas temperature sensing means (STH2) for sensing the temperature of a discharge gas of the low stage side compressor (31A, 31B, 131A, 131B) in the low stage side refrigerant circuit (103A, 103B); the expansion valve control means (16) being set to calculate a first amount of change of opening (xcex94EV11, xcex94EV21) based on the high pressure in the low stage side refrigerant circuit (103A, 103B), calculate a second amount of change of opening (xcex94EV2) based on the superheating degree sensed by the superheating degree detecting means (27) and change the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2); and a setting change means (23c) for calculating an amount of increase of opening (xcex94EV13, xcex94EV23) based on the temperature sensed by the discharge gas temperature sensing means (STH2) when the sensed temperature is equal to or above a predetermined temperature and then changing the setting of the expansion valve control means (16) so that the expansion valve control means (16) changes the opening of the motor-operated expansion valve (EVL1, EVL2) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) and additionally the amount of increase of opening (xcex94EV13, xcex94EV23)
With this arrangement, the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) is changed in principle based on the first amount of change of opening (xcex94EV11, xcex94EV21) calculated based on the high pressure in the low stage side refrigerant circuit (103A, 103B) and the second amount of change of opening (xcex94EV2) calculated based on the superheating degree of the suction gas in the high stage side refrigerant circuit (120). When the temperature of the discharge gas of the low stage side compressor (31A, 31B, 131A, 131B) is equal to or above the predetermined temperature, the opening of the motor-operated expansion valve (EVL1, EVL2) is changed based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) exceptionally considering the amount of increase of opening (xcex94EV13, xcex94EV23) based on the temperature of the discharge gas.
An eighth invention is concerned with the first invention, wherein the system further comprises: a superheating degree detecting means (27) for sensing the superheating degree of a suction gas refrigerant of the high stage side compressor (121) in the high stage side refrigerant circuit (120); a discharge gas temperature sensing means (STH1) for sensing the temperature of a discharge gas refrigerant of the high stage side compressor (121) in the high stage side refrigerant circuit (120); the expansion valve control means (16) being set to calculate a first amount of change of opening (xcex94EV11, xcex94EV21) based on the high pressure in the low stage side refrigerant circuit (103A, 103B), calculate a second amount of change of opening (xcex94EV2) based on the superheating degree sensed by the superheating degree detecting means (27) and change the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2); and a setting change means (23c) for calculating an amount of increase of opening (xcex94EV4) based on the temperature sensed by the discharge gas temperature sensing means (STH1) when the sensed temperature is equal to or above a predetermined temperature and then changing the setting of the expansion valve control means (16) so that the expansion valve control means (16) changes the opening of the motor-operated expansion valve (EVL1, EVL2) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) and additionally the amount of increase of opening (xcex94EV4) With this arrangement, the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) is changed in principle based on the first amount of change of opening (xcex94EV11, xcex94EV21) calculated based on the high pressure in the low stage side refrigerant circuit (103A, 103B) and the second amount of change of opening (xcex94EV2) calculated based on the superheating degree of the suction gas in the high stage side refrigerant circuit (120). When the temperature of the discharge gas of the high stage side compressor (121) is equal to or above the predetermined temperature, the opening of the motor-operated expansion valve (EVL1, EVL2) is changed based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) exceptionally considering the amount of increase of opening (xcex94EV4) based on the temperature of the discharge gas.
A ninth invention is concerned with the first invention, wherein the system further comprises: a superheating degree detecting means (27) for sensing the superheating degree of a suction gas refrigerant of the high stage side compressor (121) in the high stage side refrigerant circuit (120); a discharge gas temperature sensing means (STH1) for sensing the temperature of a discharge gas of the high stage side compressor (121) in the high stage side refrigerant circuit (120); a wet state detecting means (22a) for determining whether the suction gas refrigerant of the high stage side compressor (121) in the high stage side refrigerant circuit (120) is in a wet state based on preset determination conditions and outputting a predetermined wet state signal upon detection of the wet state; the expansion valve control means (16) being set to calculate a first amount of change of opening (xcex94EV11, xcex94EV21) based on the high pressure in the low stage side refrigerant circuit (103A, 103B), calculate a second amount of change of opening (xcex94EV2) based on the superheating degree sensed by the superheating degree detecting means (27) and change the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2); and a setting change means (23c) for calculating an amount of decrease of opening (xcex94EV5) based on the wet state upon receipt of the wet state signal from the wet state detecting means (22a) and then changing the setting of the expansion valve control means (16) so that the expansion valve control means (16) changes the opening of the motor-operated expansion valve (EVL1, EVL2) based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) and additionally the amount of decrease of opening (xcex94EV5).
With this arrangement, the opening of the motor-operated expansion valve (EVL1, EVL2) of the high stage side refrigerant circuit (120) is changed in principle based on the first amount of change of opening (xcex94EV11, xcex94EV21) calculated based on the high pressure in the low stage side refrigerant circuit (103A, 103B) and the second amount of change of opening (xcex94EV2) calculated based on the superheating degree of the suction gas in the high stage side refrigerant circuit (120). When the suction gas of the high stage side compressor (121) is in a wet condition, the opening of the motor-operated expansion valve (EVL1, EVL2) is changed based on the first amount of change of opening (xcex94EV11, xcex94EV21) and the second amount of change of opening (xcex94EV2) exceptionally considering the amount of decrease of opening (xcex94EV5) based on the wet state.
A tenth invention is concerned with the first invention, wherein the system further comprises an opening change means (22d) for sensing the opening of the motor-operated expansion valve (12) and causing the expansion valve control means (16) to change the amount of change of opening according to the sensed opening to increase the amount of change of opening when the opening is large or decrease the amount of change of opening when the opening is small.
With this arrangement, the amount of change of opening is reset at a relatively large value when the opening of the motor-operated expansion valve (12) is large, or reset at a relatively small value when the opening of the motor-operated expansion valve (12) is small. This results in preventing the motor-operated expansion valve (12) from being excessively opened and closed.
An eleventh invention is concerned with the first invention, wherein the system further comprises: an accumulator (24) provided between the refrigerant heat exchanger (5) and the suction side of the high stage side compressor (18) in the high stage side refrigerant circuit (3); and an opening change means (22d) for sensing a change in the opening of the motor-operated expansion valve (12) and causing the expansion valve control means (16) to change the amount of change of opening according to increase/decease in the sensed opening to decrease the amount of change of opening when the opening is increased or increase the amount of change of opening when the opening is decreased.
With this arrangement, the amount of change of opening is reset at a relatively small value when the opening of the motor-operated expansion valve (12) is increased, or reset at a relatively large value when the opening of the motor-operated expansion valve (12) is decreased. This results in preventing excessive liquid storage in the accumulator (24).
A twelfth invention is concerned with the first invention, wherein the refrigerant heat exchanger is constituted by a plate-type heat exchanger (5).
With this arrangement, since the plate-type heat exchanger has a characteristic of difficulty in providing superheat to the refrigerant at the outlet thereof, the effects of the first invention can be remarkably shown.
As seen from the above, according to the first invention, since the motor-operated expansion valve of the high stage side refrigerant circuit is controlled so that the high pressure in the low stage side refrigerant circuit reaches the predetermined target high pressure, operation of the high stage side refrigerant circuit can be directly controlled in accordance with operating conditions of the low stage side refrigerant circuit thereby improving operational responsiveness of the high stage side refrigerant circuit. Further, since the high pressure in the low stage side refrigerant circuit can be directly adjusted, a high-efficiency cooling operation can be provided. Furthermore, since the high stage side refrigerant circuit can immediately follow up an abrupt load change of the low stage side refrigerant circuit, unsuitable operation of the protective device of the low stage side refrigerant circuit can be obviated. Particularly for the so-called multi-system formed by composing the low stage side refrigerant circuitry of a plurality of pipelines, the load variation of the low stage side refrigerant circuit is extremely large and therefore the effects of the present invention can be exerted more remarkably.
According to the second invention, since the target high pressure is adequately set based on the temperature of the substance to be cooled, the high pressure in the low stage side refrigerant circuit can be set adequately in accordance with load variations to improve the efficiency of the system even if the temperature in the cold storage has extremely risen as caused, for example, at the shipping and receipt of goods or after defrosting. Further, even if the load is changed depending upon the type of the substance to be cooled, for example, even if the in-storage temperature setting to the cold storage is changed depending upon the type of goods therein, the target high pressure can be set adequately. This enables high-efficiency operation.
According to the third invention, even if the low stage side refrigerant circuit has remarkably increased in load as caused, for example, when the evaporator has frosted, the target high pressure in the low stage side refrigerant circuit can be set adequately at a suitable value. Accordingly, the high pressure in the low stage side refrigerant circuit can be held at the suitable value at any time thereby improving the efficiency of the system.
According to the fourth invention, since the target high pressure is set based on the temperature of the substance to be cooled when the operation is in a transient state or set based on the low pressure in the low stage side refrigerant circuit when the operation is steady, this prevents the target high pressure from abruptly changing when the operation is in a transient state and therefore provides stable operation.
According to the fifth or sixth invention, since the motor-operated expansion valve is controlled also considering the superheating degree of the suction gas in the high stage side refrigerant circuit, the high pressure in the low stage side refrigerant circuit can be held at a suitable value while protecting the high stage side compressor in the high stage side refrigerant circuit even under severe service conditions, such as when the evaporator has excessively frosted.
According to the seventh invention, even if the temperature of the discharge gas of the low stage side compressor has excessively increased, the low stage side compressor can be protected thereby enhancing system reliability.
According to the eighth invention, even if the temperature of the discharge gas of the high stage side compressor has excessively increased, the high stage side compressor can be protected thereby enhancing system reliability.
According to the ninth invention, since liquid back of the high stage side compressor can be obviated even in a transient operating state or under severe service conditions, this enhances system reliability.
According to the tenth invention, since the amount of change of opening of the motor-operated expansion valve is changed according to the opening, this prevents the motor-operated expansion valve from being excessively opened and closed resulting in facilitating implementation of stable control.
According to the eleventh invention, since the opening change of the motor-operated expansion valve is made relatively slowly for control in its opening direction or made relatively rapidly for control in its closing direction, this prevents excessive liquid storage into the accumulator resulting in facilitating implementation of stable control.
According to the twelfth invention, since the refrigerant heat exchanger is constituted by a plate-type heat exchanger, the effects of the first invention can be exerted more remarkably.